It is well-known to provide covers for drinking containers to prevent the spillage of the contents of the container. Many prior art covers incorporate an opening in the top of the cover in order to allow drinking of the contents either in the normal drinking fashion or by the insertion of a straw. Some covers utilize a releasable drinking flap in order to prevent the sloshing of the contents out of the containers. Other covers have an opening which is sealed by a depressible tab such that when the tab is depressed, the opening is unsealed for either drinking the contents of the container or for the pouring of the contents from the container.
As discussed hereinabove, lids have been proposed having preformed openings therein which permit the contents of the container to be drank through the opening or the contents to be poured from the container without removing the lid. However, in many proposed designs, the opening is positioned in a manner such that when the container is full, the contents may be readily spilled therefrom if the container is jarred even the slightest. In an effort to overcome the spillage problems consumption of the contents of the container by the consumer is difficult due to the positioning of the opening. In an effort to overcome the aforementioned shortcomings, the lid design set forth in U.S. Pat. No. 4,441,624 issued to Sokolowski discloses a drinking cover for a beverage container including a circular wall and annular side wall which is sealingly received on a respective container. In this instance, the top wall is tapered downwardly from front to back and includes an opening therein which is covered by a sealing flap which is positioned on the inside of the top wall of the cover. When pressure from the user's mouth is placed about the opening in the top wall, the sealing flap is displaced from the opening permitting the contents of the container to be poured therefrom. However, manufacturer of such a lid requiring a two-piece construction is both complicated and expensive and results in a lid design which is cumbersome and difficult to use by the consumer.
A similar lid design disclosed in U.S. Pat. No. 4,589,569 issued to Clements includes a lid construction having an annular mounting portion for engaging the lip of a respective cup as well as an annular side wall similar to that discussed hereinabove. Additionally, a recess for receiving the lip of the consumer is provided in a top surface of the lid to allow the consumer to grip the portion of the lid adjacent the drink-thru opening formed in the top wall. Such lids are generally manufactured using a thermoforming process wherein a softened plastic blank is vacuum formed to a die thereby conforming the blank to the shape of the die. This process may be similar to that set forth in U.S. Pat. No. 3,928,523 issued to Ward et al.
Therein, a method for molding a thermoformable plastic sheet is set forth wherein the thermoformable plastic sheet is formed over a male die which includes a plurality of passages which permits air trapped between the sheet and die to escape and/or which may be connected to a vacuum source for reducing the pressure within the passages. With the lid configurations discussed hereinabove, such a process is sufficient in forming these lids. Particularly, with the lid of Clements, because there is no plug fit and thus no substantial trough between the raised dome side wall and the annular sealing ridge, the problems presently experienced do not occur. Specifically, when forming lids of the type disclosed in U.S. application Ser. No. 467,718 filed Jun. 6, 1995, the contents of which are hereby incorporated herein by reference, having a domed top surface and plug fit, the material in the plug fit area is thinned to the point where the lid would collapse when the load necessary to secure the lid to the cup was applied to the domed lid. Accordingly, the process and apparatus set forth in detail hereinbelow becomes particularly useful when forming lids of this type.
Clearly, there is a need for a method and apparatus for forming a disposable drink-thru lid having a domed surface and which can be applied to a cup in a plug fit manner without the lid collapsing under the load applied thereto.